Alkaline earth halide-rare earth fluoride phosphor

ABSTRACT

A phosphor having a general formula; 
     
         nReF.sub.3.mAfCl:Eu.sub.x 
    
     where 
     &#34;Re&#34; is a rare earth element, 
     &#34;A&#34; is an alkaline earth element, 
     &#34;x&#34; is not smaller than 1×10 -4  and not larger than 1, and 
     &#34;n/m&#34; is not smaller than 1×10 -3  and not larger than 7×10 -1 . 
     Further addition of samarium enables the phosphor to exhibit a decreased afterglow.

BACKGROUND OF THE INVENTION

This invention relates to a phosphor consisting of an alkaline earthhalide and a rare earth fluoride and activated by europium.

It was customary in the past to use CaWO₄ as a fluorescent material forforming an X-ray intensifying screen. Further, various fluorescentmaterials have been proposed to date for improving the sensitivity ofthe X-ray intensifying screen. For example, Canadian Pat. No. 896453discloses an alkaline earth halide phosphor such as BaFCl:Eu. In thisphosphor, however, it is difficult to add divalent europium as anactivator even if firing is carried out under neutral or reducingconditions, resulting in that the produced phosphor tends to emit lightshifting a longer wavelength side because of the presence of trivalenteuropium. In short, the alkaline earth halide phosphor of this type isdefective in that a state firing condition is difficult to determine.

SUMMARY OF THE INVENTION

An object of this invention is to provide a fluorescent materialemitting light of a higher brightness than that of the light emitted byCaWO₄ and suitable for forming an X-ray intensifying screen andfluorescent screens for a cathode ray tube, a mercury discharge lamp,etc.

Another object is to provide a novel phosphor based on an alkaline earthhalide to which is added a divalent europium as an activator.

According to this invention, there is provided a phosphor emitting lightof an increased brightness and having a general formula,

    nReF.sub.3.mAX.sub.2 :Eu.sub.x                             ( 1)

where,

"Re" is at least one element selected from the group consisting of La,Gd, Y and Lu,

"A" is at least one element selected from the group consisting of Ba, Srand Ca,

"X" is at least one element selected from the group consisting of F, Cland Br,

"x" is not smaller than 1×10⁻⁴ and not larger than 1 (1×10⁻⁴ ≦x ≦1), and

"n/m" is not smaller than 1×10⁻³ and not larger than 7×10⁻ 1 (1×10⁻³≦n/m≦7×10⁻ 1).

Preferably, samarium is added to the phosphor of the formula (1),thereby decreasing the afterglow of the phosphor. Namely, this inventionalso provides a phosphor of a general formula;

    nReF.sub.3. mAX.sub.2 :Eu.sub.x.Sm.sub.y                   ( 2)

where,

"Re", "A", "X", "x" and "n/m" are the same as in the formula (1), and

"y" ranges between 1×10⁻⁴ and 1×10⁻¹ (1×10⁻⁴ ≦y≦1×10⁻¹).

The phosphor of the formula (2) is substantially equal to that of theformula (1) in brightness of the emitted light and is lower than that ofthe formula (1) in afterglow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the distribution curve of relative energy forthe spectrum of light emitted by a phosphor of the formula (1) excitedby X-ray;

FIG. 2 is a graph showing the relationship between the Eu²⁺concentration (x) and the relative brightness under X-ray excitation ofa phosphor of 0.1LaF₃.0.9BaFCl:Eu_(x) ;

FIG. 3 is a graph showing the relationship between the molar ratio (n/m)and the relative brightness under X-ray excitation of a phosphor ofnLaF₃.mBaFCl:Eu₀.01 ;

FIG. 4 is a graph showing the relationship between the Sm concentration(y) and the relative brightness under X-ray excitation of a phosphor of0.1LaF₃.0.9BaFCl:Eu₀.03.Sm_(y) ; and

FIG. 5 is a cross sectional view of an X-ray intensifying screen mountedto a cassette of an X-ray photofilm.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

It is possible to add stably a divalent europium acting as an activatorto a phosphor by reacting a rare earth fluoride with an alkaline earthhalide providing the base material of the phosphor. As a result, thephosphor of this invention emits light of an increased brightness and issuitable for forming an X-ray intensifying screen and fluorescentscreens for a cathode ray tube, a mercury discharge lamp, etc.

A phosphor of the formula (1), for example, 0.1LaF₃.0.9BaFCl:Eu₀.03emits a strong light having a peak at about 385 nm as shown in FIG. 1.The brightness of the light under X-ray excitation reaches 5 to 6 timesas high as that of the light emitted by a conventional phosphor ofCaWO₄. When excited by ultraviolet rays having a wavelength of 2,537 A,the brightness of the light emitting by the above-noted phosphor of thisinvention is 3 times as high as that of the light emitted by aconventional phosphor of (Sr.Mg)₂ P₂ O₇ :Eu. Further, the brightness ofthe light emitted by the phosphor of the formula (1 ) under cathode rayexcitation is 3 times as high as that of the light emitted by CaWO₄.When excited by X-rays, even the matrix of the phosphor of the formula(1) emits light about 3 times as bright as that emitted by CaWO₄.

FIG. 2 shows a relative brightness under X-ray excitation with respectto the molar concentration (x) of an activator Eu²⁺ for the case whereEu²⁺ is added to a base material of 0.1LaF₃.0.9BaFCl. It is seen thatthe relative brightness is increased where the molar concentration ofEu²⁺ ranges between 1×10⁻⁴ and 1. The curve of FIG. 2 remains unchangedeven if the matrix composition is varied within the scope of the formula(1). FIG. 2 clearly shows that a more preferred molar concentration ofEu²⁺ per 1 mol of the matrix ranges between 1×10⁻³ and 3×10⁻¹.

FIG. 3 shows a relative brightness under X-ray excitation for the casewhere the ratio of mols (n) of LaF₃ to mols (m) of BaFCl is changed,with the Eu²⁺ concentration set constant at, for example, 1×10⁻² mol.The curve of FIG. 3 remains unchanged even if the matrix composition andthe Eu²⁺ concentration are varied within the scope of the formula (1).FIG. 3 clearly shows that a preferred molar ratio (n/m) ranges from1×10⁻³ to 7×10⁻¹.

A phosphor of the formula (2) is just the same as that of the formula(1) except that the former is markedly lower in afterglow than thelatter. Namely, the Sm addition causes no substantial light emission ofthe phosphor. A phosphor of the formula (2) is lower in afterglow levelthan the conventional phosphor of CaWO₄. FIG. 4 shows a relativebrightness under X-ray excitation for the case where Sm has been addedto a phosphor of the formula (1), for example, 0.1LaF₃.0.9BaFCl:Eu₀.03.It is seen that a preferred molar concentration of Sm relative to 1 molof the matrix ranges from 1×10⁻⁴ to 1×10⁻¹.

The phosphor of this invention can be produced by a conventional methodsuch as hot solid phase reactions or coprecipitation of halides,followed by a heat treatment. For example, an aqueous suspension isprepared first which contains an ReF₃ compound, an AX₂ compound ("Re","A" and "X" being the same as defined previously), a halide of Eu and,as required, a halide of Sm. The suspension has been dried at atemperature of 50 to 250° C., and then subjected to firing at 600 to1,000° C., thereby producing the aimed product of phosphor.

The phosphor of this invention having the general formula (1) or (2)emits light having a peak at about 385 nm, high in brightness and low inafterglow and, thus, is suitable for forming an X-ray intensifyingscreen and flourescent screens of a cathode ray tube and a mercurydischarge lamp, etc.

FIG. 5 shows an X-ray photo cassette in which is mounted an X-rayintensifying screen. As shown in the drawing, an X-ray photofilm 1 andX-ray intensifying screens 2 disposed on both sides of the film 1 aremounted between a lid 5 and a bottom 6 of the cassette. The X-rayintensifying screen 2 comprises a substrate 4 and a layer 3 of aphosphor of this invention laminated on the substrate 4. The X-raysensitivity of the X-ray intensifying screen is 3 times as high as thatof an X-ray intensifying screen using CaWO₄. Where a phosphor of theformula (2) is used, the X-ray intensifying screen 2 is substantiallyfree from afterglow.

Described in the following are Examples of this invention. Examples 1 to12 relate to phosphors of the formula (1).

EXAMPLE 1

A mixture of LaF₃ (5 g), BaF₂ (16.5 g), BaCl₂ (26.5 g) and EuF₃ (0.5 g)was powdered and, then, subjected to firing in a quartz crucible for 1hour at 700° to 850° C. under a reducing atmosphere like H₂ gasatmosphere. The resultant phosphor had a composition of0.1LaF₃.0.9BaFCl:Eu₀.01 and, when excited by X-rays of 80 KV.2 mA,emitted light having a peak at 385 nm and brightness 6 times as high asthat of the light emitted by CaWO₄. Further, when excited by ultravioletrays having a wavelength of 2,537 A, the phosphor emitted light 3 timesas bright as the light emitted by (Mg.Sr)P₂ O₇ :Eu. Still further, afluorescent screen prepared by using the resultant phosphor exhibited asensitivity 5 times as high as that of a CaWO₂ fluorescent screen.

EXAMPLE 2

The same procedures as in Example 1 were followed except that used was amixture consisting of YF₃ 0.5H₂ O (3.8 g), BaF₂ (16.5 g), BaCl₂ (26.5 g)and EuF₃ (0.5 g). The produced phosphor has a composition of0.1YF₃.0.9BaFCl:Eu₀.01 and, when excited by X-rays, emitted light 5times as bright as the light emitted by CaWO₄.

EXAMPLE 3

A mixture of GdF₃ (5.3 g), BaF₂ (16.5 g), BaCl₂ (26.5 g) and EuF₃ (0.5g) was powdered and, then, subjected to firing for 1.5 hours at 800° C.under a weak reducing atmosphere like a mixed gas atmosphere of H₂ andN₂. The produced phosphor had a composition of 0.1GdF₃.0.9BaFCl:Eu₀.01and, when excited by X-rays, emitted light 5 times as bright as thelight emitted by CaWO₄.

EXAMPLE 4

An aqueous suspension was prepared first by adding LaF₃ (5 g) and BaF₂(16.5 g) to water. Then, BaCl₂ (26.5 g) and EuF₃ (0.05 g) were dissolvedin the suspension, followed by drying at 150° C. and subsequent step offiring for 1 hour at 800° C. under a reducing atmosphere. The resultantphosphor had a composition of 0.1LaF₃.0.9BaFCl:Eu₀.001 and emitted lighthaving a peak at 385 nm. The brightness of the light under X-rayexcitation was 3 times as high as that of the light emitted by CaWO₄.

EXAMPLE 5

The same procedures as in Example 3 were followed except that used was amixture of LaF₃ (14.7 g), BaF₂ (17.6 g), BaCl₂ (26.5 g) and EuF₃ (1.5g). The resultant phosphor had a composition of 0.3LaF₃.0.7BaFCl:Eu₀.03and, when excited by X-rays, emitted light 2 times as bright as thelight emitted by CaWO₄.

EXAMPLE 6

A mixture of LaF₃ (19.5 g), SrF₂ (12.5 g), BaCl₂ (17.5 g) and EuF₃ (0.6g) was powdered and, then, subjected to firing in a quartz crucible for1 hour at 850° C. under a weak reducing atmosphere. The resultantphosphor had a composition of LaF₃.2(Sr₀.5.Ba₀.5)FCl:Eu₀.03 and, whenexcited by ultraviolet rays (2,537 A in wavelength), emitted light 2times as bright as the light emitted by (Sr.Mg)P₂ O₇ :Eu. Further, afluorescent screen prepared by using the resultant phosphor exhibited asensitivity 2 times as high as that of a screen prepared by using CaWO₄.Still further, when excited by electron beams, the resultant phosphoremitted light 4 times as bright as the light emitted by Ca₂ MgSiO₇ :Ce.

EXAMPLE 7

A mixture of LaF₃ (39.2 g), CaF₂ (2.93 g), CaCl₂ (6.28 g), BaF₂ (112 g),BaCl₂ (133 g), SrF₂ (5 g), SrCl₂ (6.3 g) and EuF₃ (6 g) was powderedand, then, subjected to firing for 1 hour at 850° C. under a reducingatmosphere. The resultant phosphor had a composition of0.2LaF₃.0.8(Ca₀.1.Ba₀.8.Sr₀.1)FCl:Eu₀.03 and, when excited byultraviolet rays (2,537 A in wavelength), emitted light 2 times asbright as the light emitted by (Sr.Mg)P₂ O₇ :Eu.

EXAMPLE 8

A mixture of GdF₃ (42.8 g), CaF₂ (2.93 g) CaCl₂ (6.28 g), SrF₂ (5 g),SrCl₂ (6.3 g), BaF₂ (112 g), BaCl₂ (133 g) and EuF₃ (6 g) was powderedand, then, subjected to firing for 1 hour at 800° C. under a weakreducing atmosphere. The material thus treated was powdered again andheated for 1 hour at 750° C. under a reducing atmosphere. The resultantphosphor had a composition of 0.2GdF₃.08(Ca₀.1.Sr₀.1.Ba₀.8 (FCl:Eu₀.03and, when excited by ultraviolet rays (2,537 A in wavelength), emittedlight 5 times as bright as the light emitted by (Sr.Mg)P₂ O₇ :Eu.Further, a fluorescent screen prepared by using the resultant phosphorexhibited a sensitivity 4 times as high as that of a screen using CaWO₄,when excited by X-rays (80 KV.2 mA).

EXAMPLE 9

A mixture of LuF₃ (4.26 g), BaF₂ (16.5 g), BaCl₂ (26.5 g) and EuF₃ (0.5g) was powdered and, then, subjected to firing for 2 hours at 750° C.under a weak reducing atmosphere. The resultant phosphor had acomposition of 0.1LuF₃.09BaFCl:Eu₀.01 and, when excited by X-rays,emitted light 3 times as bright as the light emitted by CaWO₄.

EXAMPLE 10

A mixture of LaF₃ (39 g), LuF₃ (46.2 g), BaF₂ (70.1 g), BaCl₂ (83.2 g)and EuF₃ (2.1 g) was powdered and, then, subjected to firing for 1 hourunder a weak reducing atmosphere at 750° C. to 800° C. The resultantphosphor had a composition of 0.2(La₀.5.Lu₀.5)F₃.0.8BaFCl:Eu₀.01 and,when excited by X-rays, emitted light 4 times as bright as the lightemitted by CaWO₄.

EXAMPLE 11

The same procedures as in Example 10 were followed except that used wasa mixture of LaF₃ (17.6 g), GdF₃ (19.3 g), YF₃.0.5H₂ O (18.6 g), BaF₂(61.3 g), BaCl₂ (72.9 g) and EuF₃ (6.3 g). The resultant phosphor had acomposition of 0.3(La₀.3.Gd₀.3.Y₀.4).0.7BaFCl:Eu₀.03 and, when excitedby X-rays, emitted light 5 times as bright as the light emitted byCaWO₄.

EXAMPLE 12

The same procedures as in Example 10 were followed except that used wasa mixture of YF₃.0.5H₂ O (12.4 g), GdF₃ (25.7 g), BaF₂ (70.1 g), BaCl₂(83.3 g) and EuF₃ (11.45 g). The resultant phosphor had a composition of0.2(Y₀.4.Gd₀.6).0.8GaFCl:Eu₀.05 and, when excited by X-rays, emittedlight 6 times as bright as the light emitted by CaWO₄.

The following Examples 13 to 24 relate to phosphors of the generalformula (2).

EXAMPLE 13

A mixture of LaF₃ (19.5 g), BaF₂ (78.7 g), BaCl₂ (93.6 g), EuF₃ (2.1 g)and SmCl₃ (0.77 g) was powdered and, then, subjected to firing in aquartz crucible for 1 hour at 800° C. under a weak reducing atmosphere.The material thus treated was further heated for 1 hour at 850° C. undera reducing atmosphere, followed by cooling so as to obtain a phosphor of0.1LaF₃.0.9BaFCl:Eu₀.01.Sm₀.003. A fluorescent screen prepared by usingthe resultant phosphor exhibited a sensitivity 5 times as high as thatexhibited by a CaWO₄ screen and was lower in afterglow level than CaWO₄.Further, when excited by ultraviolet rays (2,537 A in wavelength), theresultant phosphor emitted light 3 times as bright as the light emittedby (Mg.Sr)P₂ O₇ :Eu.

EXAMPLE 14

A mixture of YF₃.0.5H₂ O (15.4 g), BaF₂ (78.7 g), BaCl₂ (93.6 g), EuF₂(4.2 g) and SmCl₃ (1.3 g) was powdered and, then, subjected to firing ina quartz crucible for 1 hour under a weak reducing atmosphere at 700° C.to 800° C. The resultant phosphor had a composition of01YF₃.0.9BaFCl:Eu₀.02.Sm₀.005 and, when excited by X-rays, emitted light5 times as bright as CaWO₄. Further, the resultant phosphor was lower inafterglow level than CaWO₄.

EXAMPLE 15

The same procedure as in Example 3 were followed except that used was amixture of GdF₃ (21.4 g), BaF₂ (78.7 g), BaCl₂ (93.6 g), EuF₃ (6 g) andSmCl₃ (1.3 g). The resultant phosphor had a composition of0.1GdF₃.0.9BaFCl:Eu₀.03 .Sm₀.005 and, when excited by X-rays, emittedlight 5 times as bright as the light emitted by CaWO₄. Further, theresultant phosphor was substantially equal to CaWO₄ in afterglow level.

EXAMPLE 16 An aqueous suspension was prepared first by adding LaF₃ (19.5g) and BaF₂ (78.7 g) to water. Then, BaCl₂ (93.6 g) was dissolved in thesuspension, followed by drying at 150° C. and subsequently mixing EuF₃(0.2 g) and SmCl₃ (0.12 g) into the dried material. Finally, thematerial thus treated was subjected to firing in a quartz crucible for 1hour at 800° C. under a reducing atmosphere. The resultant phosphor hada composition of 0.1LaF₃.0.9BaFCl:Eu₀.001.Sm₀.0003 and emitted a stronglight having a peak at 385 nm. The brightness of the light emitted bythe resultant phosphor under X-ray excitation was 3 times as high asthat of the light emitted by CaWO₄. EXAMPLE 17

A mixture of LaF₃ (58.5 g), BaF₂ (61 g), BaCl₂ (73 g), EuF₃ (6 g) andSmCl₃ (1.28 g) was powdered and, then subjected to firing for 1.5 hoursunder a weak reducing atmosphere at 750° C. to 800° C. The resultantphosphor had a composition of 0.3LaF₃.0.7BaFCl:Eu₀.03.Sm₀.005 and, whenexcited by X-rays, emitted light 2 times as bright as the light emittedby CaWO₄. Further, the resultant phosphor was substantially equal toCaWO₄ in afterglow level.

EXAMPLE 18

A mixture of LaF₃ (195.5 g), SrF₂ (125.6 g), BaCl₂ (208 g), EuF₃ (6.3 g)and SmCl₃ (0.25 g) was powdered and, then, subjected to firing in aquartz crucible for 1 hour at 850° C. under a weak reducing atmosphere.The resultant phosphor had a composition ofLaF₃.2(Sr₀.5.Ba₀.5)FCl:Eu₀.03.Sm₀.001 and, when excited by ultravioletrays (2,537 A) in wavelength), emitted light 2 times as bright as thelight emitted by (Sr.Mg)P₂ O₇ :Eu. A fluorescent screen prepared byusing the phosphor exhibited a sensitivity 2 times as high as thatexhibited by a CaWO₄ screen. Further, when excited by electron beams,the resultant phosphor emitted light 4 times as bright as the lightemitted by Ca₂ MgSiO₇ :Ce.

EXAMPLE 19

A mixture of GdF₃ (42.8 g), CaF₂ (3.1 g), CaCl₂ (4.4 g), SrF₂ (5 g),SrCl₂ (6.3 g), BaF₂ (56 g), BaCl₂ (66 g), EuF₃ (6.2 g) and SmCl₃ (0.128g) was powdered and, then, heated for 1 hour at 750° C. to 800° C. Thematerial thus treated was powdered again and heated for 1 hour at 750°C. under a reducing atmosphere. The resultant phosphor had a compositionof 0.2GdF₃.0.8(Ca₀.1.Sr₀.1.Ba₀.8)FCl:Eu₀.03.Sm₀.0005 and, when excitedby ultraviolet rays (2,537 A in wavelength), emitted light 5 times asbright as the light emitted by (Sr.Mg)P₂ O₇ :Eu. A fluorescent screenprepared by using the phosphor exhibited a sensitivity 4 times as highas that of a CaWO₄ screen, when excited by X-rays (80 KV.2 mA).

EXAMPLE 20

The same procedures as in Example 7 were followed except that used was amixture of LaF₃ (39 l g), CaF₂ (4.4 g), CaCl₂ (3.1 g), SrF₂ (5 g), SrCl₂(6.3 g), BaF₂ (56 g), BaCl₂ (66.5 g), EuF₃ (6.27 g) and SmCl₃ (0.256 g).The resultant phosphor had a composition of0.2LaF₃.0.8(Ca₀.1.Sr₀.1.Ba₀.8)FCl:Eu₀.03.Sm₀.01 and, when excited byultraviolet rays (2,537 A in wavelength), emitted light 2 times asbright as the light emitted by (Sr.Mg)P₂ O₇ :Eu.

EXAMPLE 21

The same procedures as in Example 9 were followed except that used was amixture of LuF₃ (23.1 g), BaF₂ (87.5 g), BaCl₂ (104 g), EuF₃ (2.1 g) andSmCl₃ (0.077 g). The resultant phosphor had a composition of0.1LuF₃.0.9BaFCl:Eu₀.01.Sm₀.0003 and, when excited by X-rays, emittedlight 3 times as bright as the light emitted by CaWO₄.

EXAMPLE 22

A mixture of LaF₃ (39 g), LuF₃ (46.2 g), BaF₂ (70 g), BaCl₂ (83.2 g),EuF₃ (2.1 g) and SmCl₃ (0.77 g) was powdered and, then, subjected tofiring for 1 hour under a weak reducing atmosphere at 750° C. to 800° C.The resultant phosphor had a composition of0.2(La₀.5.Lu.sub..Lu₀.5)F₃.0.8BaFCl:Eu₀.01. Sm₀.003 and, when excited byX-rays, emitted light 4 times as bright as the light emitted by CaWO₄.

EXAMPLE 23

The same procedures as in Example 22 were followed except that used wasa mixture of LaF₃ (17.5 g), GdF₃ (19.2 g), YF₃.0.5H₂ O (18.5 g), BaF₂(61.3 g), BaCl₂ (72.8 g), EuF₃ (6.27 g) and SmCl₃ (2.56 g). Theresultant phosphor had a composition of0.3(La₀.3.Gd₀.3.Y₀.4)F₃.0.7BaFCl:Eu₀.03.Sm₀.01 and, when excited byX-rays, emitted light 5 times as bright as the light emitted by CaWO₄.

EXAMPLE 24

The same procedures as in Example 22 were followed except that used wasa mixture of YF₃.0.5H₂ O (12.3 g), GdF₃ (30.0 g), BaF₂ (70 g), BaCl₂(83.2 g), EuF₃ (10.45 g) and SmCl₃ (2.56 g). The resultant phosphor hada composition of 0.2(Y₀.4.Gd₀.6)F₃.0.08BaFCl:Eu₀.05 Sm₀.01 and, whenexcited by X-rays, emitted light 6 times as bright as the light emittedby CaWO₄.

All the phosphors obtained in the above Examples fall within the scopeof this invention and are suitable for forming a fluorescent screen of alow pressure mercury discharge lamp. Further, the phosphor of thisinvention exhibits good temperature characteristics, thereby providingan excellent fluorescent screen of a high pressure mercury dischargelamp. Still further, when excited by X-rays or cathode rays, thephosphor of this invention emits light brighter than the light emittedby the conventional phosphor and a fluorescent screen thereof presents aclear picture image.

What we claim is:
 1. A phosphor having the formula;

    nLaF.sub.3.mAFCl:Eu.sub.x

wherein: A is at least one element selected from the group consisting ofBa, Sr and Ca, the Eu being present in the divalent state, x is from1×10⁻⁴ to 1, and n/m is from 1×10⁻³ to 7×10⁻¹.
 2. The phosphor accordingto claim 1, wherein x is from 1×10⁻³ to 3×10⁻¹.
 3. A phosphor having ageneral formula;

    nLaF.sub.3.mAFCl:Eu.sub.x.Sm.sub.y

wherein: A is at least one element selected from the group consisting ofBa, Sr and Ca, the Eu being present in the divalent state, x is from1×10⁻⁴ to 1, n/m is from 1×10⁻³ to 7×10⁻¹, and y is from 1×10⁻⁴ to1×10⁻¹.
 4. The phosphor according to claim 3, wherein x is from 1×10⁻³to 3×10⁻¹.